P0173 Code Meaning and Next Steps

First checks take 10 to 20 minutes for the first checks. No special tools are usually needed for the first checks.

Can you keep driving?

Stop driving if any of these apply

!The engine starts stalling, losing power sharply, or refusing to start reliably.
!The check-engine light flashes or the vehicle runs extremely rough after the code appears.

If the light is steady and the vehicle still drives normally: Often yes for a short time, but fuel economy and drivability can suffer.

What to check first

Step-by-step checks

1
Safety first
Let the engine cool before checking for vacuum leaks, loose hoses, or fuel-system damage
2
Free - no tools
Check whether P0173 is accompanied by bank 1 fuel-trim or misfire codes, because shared causes are common
3
Basic tool needed
Inspect vacuum hoses, intake ducting, and PCV plumbing for splits, loose clamps, or anything disconnected
4
Basic tool needed
Notice whether the engine runs rough at idle, under load, or only in certain temperature conditions
5
Basic tool needed
If scan data is available, compare bank 2 fuel trims with bank 1 before replacing parts

If the code returns

-If bank 2 is lean only at idle, vacuum leaks move higher on the list.
-If the issue is worse under load, fuel pressure or injector delivery deserves more attention.
-If fuel trims normalize after the leak is fixed, stop there before replacing the oxygen sensor or fuel parts.

Background

What this code means

P0173 is a generic OBD-II code for a bank 2 fuel-trim malfunction.

That means the engine computer has had to correct the air-fuel mixture too far on bank 2 and can no longer keep the mixture where it expects it to be.

Diagnosis

Common causes

Most common

Vacuum leak on bank 2 side

Unmetered air can push the mixture far enough out of range to set a fuel-trim fault.

Common

Fuel-pressure or delivery issue

Low fuel pressure or weak delivery can force the ECU to add too much correction.

Common

Injector imbalance

A weak or restricted injector on bank 2 can skew fuel trim in that direction.

Possible

Air metering fault

A bad MAF or related intake issue can affect the whole mixture picture.

Avoid these mistakes

What not to do

xDo not replace the sensor first if there is obvious wiring, connector, or fuel contamination damage.
xDo not assume a flex-fuel or fuel-temperature code is safe to ignore if hard starting or stalling is already happening.

Parts

Parts that may need replacing

PartTypical costNotes

Vacuum hose or intake duct repair$10-$120Often the cheapest and most common fix if a leak is found.

Fuel pressure regulator or pump diagnosisVariesRelevant when the engine is lean under load or fuel delivery is weak.

Injector service or replacement$50-$200 eachWorth checking if one bank is clearly fuel-starved.

Related OBD codes

P0171

P0171 usually means bank 1 is running too lean.

P0174

P0174 usually means bank 2 is running too lean.

P0300

P0300 usually means the engine is detecting random or multiple-cylinder misfires.

Source notes

Generic OBD-II (SAE J1979 / ISO 15031-5). P0173 was expanded around common bank 2 fuel-trim problems, especially vacuum leaks, delivery issues, and injector imbalance.

This guide is written as a generic multi-make reference, so bulletin history, sensor locations, and repair order can still change by manufacturer and engine family.

This is generic OBD-II guidance and should not override vehicle-specific service information. Exact diagnosis and repair steps vary by make, engine family, and model year.

Last reviewed: 2026-04-10

Reference: Open reference

P0173 - P0173 Usually Means the Fuel Trim on Bank 2 Is Out of Range